1. Field of the Invention
This invention relates to a film reader, and more particularly to a portable film reader for observing the film images projected on a reflection type screen.
Microfilm is a recording medium for recording a document, drawing or other object on a highly reduced scale, and for reading the recorded image in the film, such recorded image is projected in an enlarged form on a screen and observed by a film reader. Therefore, the overall size of the film reader unit is decided depending on the extent to which the images recorded reducedly on the film are enlarged. Generally, in case of enlarging and reading a reduced image recorded on the microfilm, it is convenient for easy and quick observation to project the image by enlarging it substantially to the original size of the object or to a size about 20 or so percent greater than the original (real-life) size, regardless of the rate of reduction of the image. Thus, the value of magnification of the enlarged and projected image is decided by the rate of reduction of the image on the film, and hence it may be said that the size of the film reader unit is determined according to the size and type of the object which is photographed in the film on a reduced scale.
Also, in the conventional film readers, a reflector alone is disposed in the light path from the projection lens to the screen on which the image is projected, and hence a large space is left in the reader unit. Therefore, a film reader using a microfilm having photographed therein a large-sized object is large in its external dimensions for its weight, and hence the entire reader assembly is enlarged in size to make it incommodious to carry about. Also, the expenses for packing and transportation run up and a large space is required for storage.
2. Description of the Prior Art
Generally, the film readers may be classified into two types according to the observation system employed. One is the "transmission" type in which an image is projected on the back of a so-called transmission type screen formed by spreading a diffusing paint on one side of a glass-made or transparent acrylic resin made plate, and the transmitted light is observed on the front side of the screen; and the other is the "reflection" type in which an image is projected on a so-called reflection type screen same as a movie screen and the reflected light is observed.
The former type, however, has drawbacks that the transmissivity is low owing to the diffusing paint, the picture is dark, the diffusivity is poor so that it is hard to read the periphery of the picture unless the viewer moves the position of his eyes, and also the picture glitters. But this type has advantages that good image contrast is obtained and also the image projected face of the screen is proof against intrusion of dust or other alien matters and also safe from cuts or other damage as the back side of the screen is hermetically shielded.
On the other hand, the latter type is free of the said defects of the former type, such as dark picture, poor diffusivity and glittering of the picture, and the picture is easy to read. This type, however, has the problem that the image projected face of the screen could gather dust or other alien matters and be damaged by intrusion of such alien matters as the front side of the screen is open.